In general, perfluoropolyether-containing compounds have water and oil repellency, chemical resistance, lubricity, parting and antifouling properties because of their very low surface energy. For the effective utilization of such properties, these compounds are widely used in the industry as water/oil repellent antifouling agents for paper and fibers, lubricants in magnetic recording media, oil repellents in precision machines, parting agents, cosmetic ingredients, and protective coatings.
The same properties, however, suggest that perfluoropolyether-containing compounds are non-tacky and non-adherent to other substrates. They are applicable to the substrate surface, but difficult to form a coating firmly bonded to the substrate.
Silane coupling agents are well known as the means for establishing a firm bond between a substrate surface such as glass or fabric and an organic compound. The silane coupling agent has an organic functional radical and a reactive silyl radical (typically alkoxysilyl radical) in a molecule. The alkoxysilyl radical undergoes self-condensation reaction with air-borne moisture, converting to a siloxane to form a coating. At the same time, the silane coupling agent forms chemical and physical bonds with the surface of glass or metal, resulting in a durable tough coating. By virtue of these advantages, the silane coupling agent is widely used as a coating agent to a variety of substrates.
As one exemplary compound which exhibits the above-mentioned characteristics, JP-A 58-167597 discloses fluoroaminosilane compounds of the following formula (2):
wherein R1 and R2 each are a C1–C4 alkyl radical, Q1 is CH2CH2CH2 or CH2CH2NHCH2CH2CH2, h is an integer of 1 to 4, and i is 2 or 3. These compounds, however, fail to fully take advantage of the perfluoropolyether radical because the perfluoropolyether radical portion is as short as consisting of two to five monomer units of hexafluoropropylene oxide (HFPO).
Also, JP-A 58-122979 discloses compounds of the following formula (3) as a water and oil repellant to be applied to glass surface.
Herein, Rf1 is a polyfluoroalkyl radical having 1 to 20 carbon atoms, which may contain at least one ether bond, R3 is hydrogen or lower alkyl, A is alkylene, X1 is —CON(R4)-Q- or —SO2N(R4)-Q- wherein R4 is lower alkyl and Q is a divalent organic radical, Z is lower alkyl, Y is halogen, alkoxy or R5COO— wherein R5 is hydrogen or lower alkyl, s is 0 or 1, t is 1, 2 or 3, and u is 0, 1 or 2. These compounds do not exert fully satisfactory effects because the number of carbon atoms in the fluorinated radical portion is as small as 1 to 20 carbon atoms.
Since many tall buildings are constructed in the recent decades, the demand for the technology for imparting “stain resistance” or “ease of stain removal” for keeping glazing maintenance-free is increasing. The same technology is also required in order that display screens be fingerprint-free for better outer appearance and visibility. There is a desire to have a material meeting such demands.
Effective utilization of the above-described characteristics of perfluoropolyether-containing compounds and silane coupling agents is desired. JP-A 9-258003 discloses a fluorinated silane compound of the formula (4) shown below as a surface treating agent which can form on the substrate surface a tough coating having excellent water and oil repellency, antifouling properties, chemical resistance, lubricity and parting properties. Specifically, the fluorinated silane compound of formula (4) forms an antifouling layer on a lens.
Herein, Rf′ is a straight or branched perfluoroalkyl radical having 1 to 16 carbon atoms, X′ is iodine or hydrogen, Y1 is hydrogen or lower alkyl, Z1 is fluorine or trifluoromethyl, R12 is a hydrolyzable radical, R13 is hydrogen or an inactive monovalent organic radical, c′, d′ and f′ each are an integer of 0 to 200, g′ is 0 or 1, p′ and q′ each are an integer of 0 to 2, and k′ is an integer of 1 to 10.
However, the fluorinated silane compounds of formula (4) are insufficiently adhesive to substrates and unsatisfactorily durable because hydrolyzable radicals are contained in a relatively large proportion, but only at one end of a molecule. When they are used as the surface treating agent to lenses, they fail to maintain the desired performance for a long term and are thus below the practically acceptable level.
Antireflection films are generally provided on the surface of viewer equipment or the like. Such antireflection films tend to receive contaminants such as hand dirt, fingerprints, sweat, saliva, hair conditioners and the like. When antireflection films are contaminated, surface reflectivity changes, or deposits are seen as white spots in relief to make display contents vague. There is the drawback that contaminants on the antireflection film become more obstructingly perceivable than on a simple transparent plate (without antireflection film). It has long been desired to have an antireflection film which is effective for preventing contaminants from depositing thereon and easy to remove contaminants if deposited.
Several antireflection films intended to improve stain resistance are known in the prior art. JP-B 6-5324 discloses an antireflection film comprising an antireflection layer consisting of a single inorganic ply or plural inorganic plies having a surface layer formed mainly of silicon dioxide by PVD, and a cured layer on the surface thereof of an organic polysiloxane base polymer or perfluoroalkyl-bearing polymer.
However, when human contaminants such as hand dirt and fingerprints deposit on this antireflection film, it is difficult to wipe off the contaminants with tissue paper. The contaminants are extended and spread to a thin film when wiped, and the antireflection film can be marred on strong rubbing. Satisfactory removal of contaminants is accomplished by no means.
Perfluoropolyether radical-bearing compounds generally have characteristics as mentioned above and are thus utilized in the art. For example, JP-A 11-29585 discloses an antireflection film including an antifouling layer of a perfluoropolyether-modified aminosilane of the formula (5):
wherein X3 is a hydrolyzable radical, R6 is lower alkyl, R7 is hydrogen or lower alkyl, Q2 is CH2CH2CH2 or CH2CH2NHCH2CH2CH2, d is an integer of 6 to 50, e is 2 or 3, b and c each are an integer of 1 to 3. This antireflection film has improved water and oil repellency, antifouling, chemical resistance, lubricity and parting properties. However, it has the problems of time-consuming curing and poor adhesion to substrates because polar radicals having a high affinity to water such as amide radicals are contained in the molecule of perfluoropolyether-modified aminosilane used in the antifouling layer and the proportion (wt %) of hydrolyzable radicals per molecule is low. The silane compound must be given further functions before it can be utilized as the surface treating agent.
JP-A 2001-188102 discloses an antireflection film including an antifouling layer of a perfluoropolyether radical-bearing silane coupling agent of the formula (6):Rf2—(OC3F6)k—O—(CF2)j—(CH2)1—O—(CH2)r—Si(OR8)3  (6)wherein Rf2 is a straight-chain or branched perfluoroalkyl radical having 1 to 16 carbon atoms, k is an integer of 1 to 50, j is an integer of 0 to 3, i is an integer of 0 to 3, r is an integer of 0 to 6, 0<j+i≦6, and R8 is C1–C10 alkyl. The perfluoropolyether radical-bearing silane coupling agent used in the antifouling layer does not contain polar radicals, but the proportion (wt %) of hydrolyzable radicals per molecule is not fully high. The problems of time-consuming curing and poor adhesion to substrates must be overcome before this silane coupling agent can be utilized as the surface treating agent.
There is a desire to have an antireflection filter which is less receptive to contaminants; which if contaminants deposit thereon, makes the contaminants to be less perceivable and makes it easy to wipe off the contaminants (including human contaminants such as hand dirt and fingerprints), is resistant to marring by the wiping operation; which if water droplets deposit thereon, is easy to shake off the droplets; and which keeps for a long term the desired functions including stain resistance, ease of wiping-off, mar resistance and water repellency.